Various types of circuits have been employed to determine the status or condition of the switch, and provide an indication of the switch condition. By way of example, U.S. Pat. No. 4,658,249, entitled "Data Communication System With Key Data Bit Denoting Significance of Other Data Bits", which issued Apr. 14, 1987 to William R. Vogt, and is assigned to the assignee of this application, includes a generalized showing of a switch state determination circuit. An improvement to that determination circuit of the '249 patent was subsequently described and claimed in an application entitled "Switch Monitoring Arrangement With Remote Adjustment Capability Having Debounce Circuitry for Accurate State Determination", filed Apr. 29, 1988, Ser. No. 188,323, which issued Aug. 1, 1989 as U.S. Pat. No. 4,853,685 in the name of William R. Vogt, and is assigned to the assignee of the present application. In addition to the remote adjustment feature described in the '685 patent a confirmation signal is produced, and stored in a latch circuit, upon verifying the status signal. This operation, coupled with the remote adjustment feature, produced a significant step forward in this art.
The systems described in the '249 patent and the '685, as well as the present invention, are useful with alarm systems using a polling technique. That is, the various transponders are interrogated, either sequentially, or in a random manner or in some other way, to determine the conditions at each transponder and/or any associated transducer. If there is a large system with many devices and transponders coupled to a single controller, it may take three seconds to complete a poll. It is possible to have a device go briefly into alarm, and emerge from the alarm condition in the time interval just after the associated transponder has been polled and previous to the next polling of that same transponder. It is possible that if more than one point or connected device goes into alarm at once, the several alarms can be cleared simultaneously without recognition at the controller of all the individual units that have been alarmed. Many systems include a "return-to-normal" or "device reset" type of clearing signal which clears all the devices and does not admit of individual identification of a plurality of alarmed units. Moreover in the daytime settings the alarm systems are usually "off", so that if an alarm is transmitted back to a central station, it is cleared by the central station. That is, the alarms are virtually ignored when the system is not activated.
Another condition which could happen in systems which include a "tamper" type of signal, and an "alarm" signal which overrides the tamper signal, can be explained in connection with a motion detector. If an individual were to walk up toward the motion detector and thus generate an alarm signal indicating movement within the protected area, he could rapidly remove the cover from the detector and effect some physical change in the circuit to allow undetected re-entry at a later time. This can occur because in many systems the tamper signal is overridden by the alarm signal.
All these shortcomings of the various systems demonstrate the need for a fire and/or burglar alarm system having switch arrangements which provide outputs such as alarm and trouble, in which after an alarm or trouble signal is given and latched, the specific devices and/or latches can be selectively cleared. It is therefore a principal consideration of the present invention to provide such an effective system for individual, selective clearing of the devices and/or latches.